View Single Post
  #1  
Old 08-04-2009, 11:58 PM
ngcles's Avatar
ngcles
The Observologist

ngcles is offline
 
Join Date: Dec 2006
Location: Billimari, NSW Central West
Posts: 1,664
Observing Report 29 March 2009 - NGCLes

Hi All,

Well it’s nearly a fortnight ago but I thought I'd post some observations made from my nearly-dark site at Bargo in highlands southwest of Sydney on the night of th 28th and morning of 29th March 2009.

There was hardly a cloud in the sky all day which only made me suspicious given the bad run of cloud we've endured over the last several months, it kinda looked like a trap -- to entice me 100km away and then when I was all set-up and ready; call in the clouds. This time there was no deception, trickery or teasingon the part of mother-nature. Particularly as it was Earth-Hour.

And, while we're on the subject of Earth-Hour, the SQM readings for the night started out at 21.1 and ended at 2am at 21.4 with a linear improvement in-between. No bumps up or down between when the lights went off or on. Just like every other Saturday night. It seems Earth-Hour made no apparent difference at all as compared to any other moonless Saturday night there.

On the other hand the seeing was wonderful -- the best I've seen from Sydney and its environs for 2 to 3 years which made Saturn a real treat
at x247, x317 and x371. We observed a shadow transit of Titan which was exquisite. With Titan sitting low in the glare of bright Saturn Titan was occasionally seen as a disc and was a clear reddish-fawn colour. I could also still see long glimpses of the Cassini division despite the rings being closed right-down.

The Homunculus was stunning at x465 with all the gross detail in the iconic Hubble image clearly visible and some of the fine detail too. Besides the dusky blobs in the brighter lobe, the edges of the brighter lobe had all sorts of lumps and dings in it -- its boundary is really quite irregular in shape.

One other surprising observation was of NGC 3918 -- the "Blue Planetary" in Centaurus nr Crux which is detailed below. I managed to get through about 40-odd galaxies in the end -- less than I expected but I 'wasted' a lot of time gawking at Saturn!


x185 27' TF

IC 2532 Galaxy *
RA: 10h 00m 05.4s Dec: -34° 13' 41"
Mag: 13.9 (P) S.B.: --- B-V: --- Size: 1.5'x1.2'
Class: (R')SB(rs)a P.A.: 38 Inclination: --- R.V.: +2900

NGC 3087 Galaxy *
RA: 09h 59m 08.8s Dec: -34° 13' 30"
Mag: 11.6 (V) S.B.: --- B-V: +1.05 Size: 2.1'x1.9'
Class: E+: P.A.: 45 Inclination: --- R.V.: +2673 Source: RC3 *

IC 2532 is found about 10' E of NGC 3087. -87 is a small, round mod bright eg in the middle of a small tri of mag 12-13 *s. Around about 1' diameter growing slightly at first to centre and then at centre steepening to a considerably brighter core zone. IC 2537 is 10' E near a small group of faint *s. For mag 13.9 it seems to be faint and LSB. Difficult to see structure, seems round, 30" diameter with a slight central brightening and has a 10th mag * just outside the N - NE halo. Possible faint spot or faint stellaring in the centre.



x185 27' TF

IC 2536 Galaxy *
RA: 10h 03m 29.8s Dec: -33° 57' 04"
Mag: 14.5 (P) S.B.: --- B-V: --- Size: 1.9'x0.4'
Class: SBc pec sp P.A.: 45 Inclination: --- R.V.: +5384 Source: RC3 *

ESO 374-23 PGC 29109 Galaxy *
RA: 10h 02m 49.9s Dec: -33° 57' 12"
Mag: 15.2 S.B.: --- B-V: --- Size: 0.9'x0.3'
Class: L P.A.: 39 Inclination: --- R.V.: --- Source: PGC *

-36 is a pretty small, edge on eg which is found in a mod well-populated field. There is a small oblong or rectangle of of mag 12 & 13 *s to the NE of the eg and the long sides of that point in the direction of -36. There is a mag 14 * not far off the S flank. Can't quite hold it consistently with DV., probably 1.5' x 15" in about PA 45 with a weak brightening to the centre.

ESO 374-23 is a similar 1/2-'scale eg in the same PA 10' westward but fainter.



x185 27' TF

IC 2539 Galaxy *
RA: 10h 04m 16.1s Dec: -31° 21' 45"
Mag: 14.0 (P) S.B.: --- B-V: --- Size: 1.9'x0.4' Class: SA(s)bc:
P.A.: 25 Inclination: --- R.V.: +2850 Source: RC3

A faint but beautiful eg, small elong lens-shaped 1.25' x 10" in about PA 30 and has not far off the SW tip ...

then see the optical transient. Exact transcript:

I've just seen something highly unusual in the eyepiece and I've got to describe it I've just seen a star brighten and fade in just a few seconds. There are three stars near the EG on the W flank at the SW end. Nearest the core is a mag 15 star, then an even fainter perhaps mag 15.5 * which is intermittently visible, and then the 12th magnitude one at the SW tip. The first of these which is visible nearly all of the time AV brightened over two or three seconds to be almost as bright as the 12th mag * at the tip. Est Mag 122.6 – 12.7, Stayed that brightness for a few seconds and then faded back to "normal" in about 1/2 the time it took to brighten. (see below the post on IIS). Total time for the event is slightly uncertain, I'd estimate 6-7 seconds, 10 at most 5 at least.

Back to the eg, it is in PA 30, with a slight broad concentration to centre but no evidence of nucleus.

The following thread here:

http://www.iceinspace.com.au/forum/s...ad.php?t=43028

refers to this apparent optical transient and the text below appears there:

Hi All,

I'm hoping for your help on this one.

Last night I was observing the small faint nearly edge-on galaxy IC 2539 in Antlia at about 9.30pm local time (10.30 UT) on 28032009 at Bargo NSW. The conditions were very good. I'd rate the seeing at 8/10 and somewhere around 0.7" or possibly slightly better. The transparency I'd rate as a 7 verging on 8/10 with a SQM-L showing a reading 10mins previous of 21.12 equating to a ZLM about 6.2. I was observing at x185 with a 12mm TII with an 18" f/4.9 with Argonavis DSC and Servocat drive and goto.

A POSS II red 5 arc-min square image of the galaxy which shows the position of the possible transient is here:

http://stdatu.stsci.edu/cgi-bin/dss_...e&fov=NONE&v3=

There were three stars near the galaxy that I could see while observing -- TYC 7170-1368-1 is on-axis with the galaxy to the SW -- about 1.4 arc-mins from a rough centre of the galaxy in PA 208 has a magnitude of 12.06. I could also see two very faint stars just off the W flank of the SW end of the galaxy. These were USNO 0525-12640582 at mag 15(??) and USNO 0525-1264033 at mag 15.75.These two are respectively -- 39" distant from centre in PA 238.9 and 56 arc-seconds in PA 225.Both of these were very faint in the eyepiece and averted vision. On the image, there is a further faint star between TYC 7170-1368-1 and USNO 0525-1264033. This is USNO 0525-12640453 (mag 16.95) and was not seen.

As I was observing the galaxy, I noticed the star USNO 0525-12640582, or at least at a position coincident with that star brightened quite a bit to become almost as bright as TYC 7170-1368-1. The apparent brightening ramped up evenly over about 3 seconds and remained apparently constant for about another 3 or 4 seconds and then faded somewhat more quickly back to "normal" in perhaps about a second. I'd estimate it reached mag 12.7 or thereabouts -- I didn't get long to make the estimate. Nothing else in the field or near the galaxy showed anything similar at the same time (or any other time) -- this was the only object to do this. No movement in the apparent transient was detected/observed while the event occurred.

I am a reasonably experienced observer. No alcohol consumed in the previous 14 days. Illicit drugs not involved. No prescription or non-prescription drugs for at least 14 days. The equivalent of 1 cup of normal strength tea consumed about 10 hrs before -- caffeine apparently not an issue. 8 hrs sleep the previous night. Had been awake just 11 hrs before making this observation. Not feeling tired at all. Had only just started "serious" observing 10 mins before.

I believe this apparent observation is of a non-spurious nature -- of course I have no back-up and there is no objective corroboration. I feel pretty confident in the observation. The event lasted at most 10 seconds, probably more like 6 or 7 and there was no time to gain confirmation from other observers. I am unable to say whether it was the star that brightened or something in the background or foreground at a coincident position caused the apparent observed brightening.

I've never seen anything like this before. Should this be reported somewhere? Is there an apparent and logical explanation?

Feel free to comment.

And including a response from Brian Skiff re this:

Hi All,

I have received a reply from the highly respected Amateur now professional astronomer Brian Skiff that was posted on AMASTRO and it seems I'm not the first person to see this type of event (not with this star though!)

"Les' star is a 4".5 pair of similar brightness on DSS and 2MASS images. The southeastern component is slightly brighter, and the2MASS colors are those of a garden-variety K0 giant or mid-K dwarf; statistically in this part of the sky it is somewhat more likely to be a dwarf rather than a giant---both very ordinary sorts of stars,
in either case, so nothing obvious about the star colour.

I have seen just this sort of phenomenon once, just as Les
has described: that is, a perfectly ordinary field star flaring up
by several magnitudes, then fading back to the previous brightness.
My event was shorter, lasting only a couple seconds total.
Looking at my observing records, the star was GSC 5706-10179 =
UCAC2 28786920 (18 54 34.75 -08 49 55.6 [J2000, UCAC2]),
which is the mag 13 star on the WSW edge of the large planetary
nebula IC 1295. My notes (1981 March 15) say the star flared by
2.5 magnitudes, then dropped back, followed by irregular flickering
for a few seconds. None of the other stars in the field (obviously
a lot of them!) did anything. I was using a 25cm Newtonian at
the time. The star has the colour of a slightly reddened K-giant,
which are ubiquitous in the Milky Way.
Back in 1981 I knew about ordinary flare stars, but knew they
didn't erupt that fast (the timescale violates light-travel-time
and simultaneity principles). But we know now about funny stuff
happening on very short timescales, but getting them to happen
around plain-vanilla stars is problematic.

Since we are only beginning to explore this time-domain in
astronomy, it is not surprising there's no ready explanation for
these sorts of observations. I dunno what's going on, but aside
from probably being more fatigued (Scutum in mid-March from the
northern hemisphere....that's 4am!), I am just as convinced as Les
of the reality of what I saw. If it was something new in the field,
you could readily invoke physio/psychological effects, but the event
occurred on an identifiable star.

Watch this space!

\Brian"

So I might not have been dreaming after all ...

It seems too short to be a flare from a flare-type star (many K-stars and most M-type stars are flare stars). They normally last many minutes and it is waaaaaaay to slow to be a micro-lens event. No explanation yet. Maybe it is a rare and as yet unknown type of event -- who knows

If you've got a suggestion, give a hoy!



x185 27' TF

IC 2538 Galaxy *
RA: 10h 03m 56.2s Dec: -34° 48' 28"
Mag: 14.6 (P) S.B.: --- B-V: --- Size: 1.5'x0.7' Class: SA(r)c pec
P.A.: 9 Inclination: --- R.V.: +8412

This eg is in a mod well populated field to the N of a mag 8 * and almost between 2 *s of mag 122.5 to 13. very small amorphous round blob of consistent SB and no central brightening.



pt 2 & 3 to follow ...
Reply With Quote